Apparatus for studying fretting fatique in vacuum

Recent investigations on the mechanism of fretting fatigue have indicated that mechanical damage, not chemical corrosion, has the largest effect in decreasing structural component life. Since there is no general agreement on the mechanism of fretting fatigue, an experiment has been designed to evaluate statistically the relative role of the mechanical process and the chemical process in reducing fatigue life. An initial step was to develop an apparatus that allows fretting fatigue tests to be performed in both laboratory air and vacuum environments. A detailed discussion of the experimental apparatus and experimental procedure are presented in this paper. Also typical test results are presented. It is found that fretting fatigue in vacuum is about ten times slower than that in laboratory air. Fractographic analysis of the wear surface indicated that less severe fretting damage occurred in the vacuum environment.